Federal prosecutors alleged two groups of Chinese nationals separately conspired over several years to steal advanced seeds from U.S. companies.

The charges, filed in U.S. courts in Des Moines, Iowa, and Kansas City, Kan., outline efforts by the Chinese nationals to target DuPont Co., Monsanto Co. and Ventria Bioscience Inc., according to court documents and industry officials. In one case, an employee of a Chinese seed company was...